This invention relates to pacemakers and has particular relationship to implantable pacemakers. An implantable pacemaker includes a primary power source and a converter for converting the output of the source into pulses for the heart and for controlling the flow of pulses to the heart. The source and converter are enclosed in a container which is implanted typically in the left-hand portion of the chest or in the abdomen. The converter supplies its pulses to the heart through a catheter. It is desirable, if not indispensible, that the pacemaker be of as light-weight and of as low volume as practicable and it is an object of this invention to provide a light-weight and low-volume pacemaker.
Purdy et al U.S. Pat. No. 3,866,616 discloses an isotopic pacemaker having a primary source of radioactive material whose heat is converted into electricity by a thermoelectric unit. The source and the thermoelectric unit and a converter, including the control, are embedded in silicone rubber. Because the primary source is of very low mass, typically about one-third gram, this pacemaker is of light-weight and low-volume, typically sixty-seven grams and thirty-three cubic centimeters.
There are also pacemakers in which the primary power source is a battery. Recently pacemakers in which the primary source is a lithium battery and which is of relatively long life has come into vogue. Typically, in a lithium battery the electrolyte is lithium iodide and the anode is lithium and the cathode is a combination of lead iodide and lithium iodide. Typically, seven banks, of three cells each in series, are connected in parallel delivering about six volts. The use of the parallel banks creates a seven-fold redundancy providing protection against failure of one or more cells. In pacemakers of this type, in accordance with the teachings of the prior art, the converter and battery is potted in EPOXY resin or the like. The potting serves to prevent the shocks, to which the pacemaker is subjected during the normal day-to-day movement and physical encounters of the host, from damaging the pacemaker. Such pacemakers have the disadvantage that their weight and the volume which they occupy is excessive.
It is an object of this invention to overcome the disadvantages of the prior art and to provide a method of making a light-weight, low-volume pacemaker whose components shall be embedded in potting which shall effectively prevent them from being damaged by shock. It is also an object of this invention to provide such a light-weight, low-volume pacemaker.